LR freeze for 10-40 seconds in develop mode

I think i've found a bug in lasts versions of LR:in develop mode, if i switch from a Nikon d800 raw to Nikon d750 raw (and viceversa) LR freeze for 10-40s. No problem if I scrolling many images from same camera at all.In library mode i haven't issue at all.

For this problem i downgrade to v7.2, after this release this bug shows up.Any idea?